A prevalent problem in planetary gear transmissions, especially automotive transmissions, is gear noise. Much of the gear noise is caused by inaccurate positioning of the receiver bores in the planet carrier and by inaccurate bore sizing. These inaccuracies also cause wear and shorten service life.
Single point tools could be used to finish the bores, but they wear relatively rapidly and do not maintain consistent bore size. Reamers are preferred, because they ream to a more consistent bore size and also because the multiple, long cutting lips of a reamer provide a much longer cutting life.
The part to be reamed usually is formed with rough holes which are not concentric with the true hole position desired. This eccentric hole stock creates cutting forces which tend to reflect a reamer out of position. Also, hole locations are affected by temperature growth in the reamer spindles which generate considerable heat from their bearings.
Floating reamers will ream holes to true size, but the eccentric stock will deflect the reamer from its correct position unless reamer guide bushings are placed in close proximity to the entrance of the holes being reamed. These bushings must be retractable to facilitate part loading and unloading. Also, the apparatus for positioning the bushings must be extremely precise.
In order to effect an even more precise hole location, and to extend the wear life of the finish reamers and bushings, it is desirable to pre-drill or ream the part in an initial roughing operation before presenting the holes for final reaming. The initial roughing operation removes excess hole stock and makes the remaining finish stock more nearly concentric with the desired hole location. The initial roughing operation should be very precise to provide optimum hole stock conditions for the final reaming operation.
Since smaller guide bushings are required for roughing than for final reaming, an additional set of guide bushings must be provided.
The initial and final operations should be carried out with the part in the same chuck, because re-chucking could result in changing the locations of the holes.
In addition, the arrangement should be such that temperature changes in the bushing positioning system will have little effect on both the hole-to-part center spacing and hole-to-hole spacing. Preferably, temperature growth should be tangential to the center of the part, thus not affecting radial distances from the center nor disturbing the hole-to-hole circumferential spacing since temperature growth will then move each hole circumferentially nearly equal amounts to maintain the set relationship.
The purpose of this invention is to provide apparatus capable of satisfying the above objectives.
Other objects and features of the invention will become more apparent as the following description proceeds, especially when considered in conjunction with the accompanying drawings.